Conventionally, various kinds of motor vehicles are equipped with automatic transmission systems which allow the operator of the vehicle to shift the transmission gears without operating the clutch, and such an automatic transmission system comprising a torque converter, a multi-disk clutch and a gear train is typically controlled by hydraulic pressure.
Such a transmission system is typically equipped with a manual valve for controlling hydraulic pressure for manual shifting, and a control shaft rotatably supported by the casing or other fixed part of the transmission system and rotated by the operation of the shift lever so as to operate the manual valve. Further, to the control shaft is integrally attached a detent cam plate having a cam surface including depressions corresponding to different shift positions of the shift lever on its free end, and the manual valve and the control shaft are accurately positioned according to each selected shift position by urging a cam follower member such as a roller against this cam surface with a spring member.
Japanese patent laid open publication No. 60-94858 discloses such a detent cam plate 24 integrally secured to a control shaft 22, and a sheet spring 25 urging a cam follower consisting of a roller 26 against a wavy cam surface 24a through 24 defined along an edge of the detent cam plate 24. Japanese utility model laid open publication No. 1-87417 discloses a similar structure which however employs a compression coil spring 15 to urge a cam follower against the cam profile of the detent cam plate 8.
However, according to such prior detent structures, the spring force urging the cam follower against the cam profile of the detent cam plate is transmitted to the control shaft, and this force is counter-acted by a radial force at an opening of the casing of the transmission system rotatably supporting the control shaft. Such a radial force at the load-bearing surface of the opening rotatably supporting the control shaft causes an increase in the resistance against the rotation of the control shaft, and, thereby, an increase in the force required to operate the shift level from the initially designed level.
Further, when the spring member for urging the cam follower against the cam profile of the detent cam plate consists of a sheet spring, it is difficult to achieve an optimum spring force since the adjustment of the spring force requires a change to be made to the dimensions of the sheet spring. A coil spring allows easy adjustment of the spring force, but using a compression coil spring involves some complication of the structure and difficulty of the assembly work.